The weaver (wv) mutant mouse is characterized by loss of most of the granule cells (GC) of the cerebellum and of the dopaminergic neurons of the substantia nigra (SN). This has caused speculation that a common molecular mechanism underlies the pathology in each cell. We propose using subtracted probes to isolate the wv gene product and then the wv gene. The molecular biology of development of the wv defect will be studied, and the chromosome-specific probes derived will be used to enrich the chromosome 16 linkage map. The study will also result in the production of GC-specific markers. Accomplishment of the objectives will be of general importance for they will result in the isolation and characterization of the wv gene and its mRNA, and of markers for normal GC and their precursors in the external germinal layer (EGL). Investigation of the expression of such markers during development in wv mutant mice will characterize the progression of disease in this degenerative condition at the molecular level. Furthermore, the wv gene is located on a portion of mouse chromosome 16 that is homologous to human chromosome 21, and the wv mutation resembles the human disease cerebelloparenchymal disorder III. The approach will include enrichment, identification and characterization of cDNA markers for GC. The methods are: 1) production and screening of cDNA libraries, particularly a wv/+ library, by subtractive and differential hybridization, 2) localization of the derived clones to chromosome 16 by Southern blotting to genomic DNA from mouse-hamster hybrids, 3) further localization to GC and SN by in situ cell hybridization and transcription and northern blot analysis, 4) characterization by sequencing. If a putative weaver gene is identified, we will produce a restriction map, isolate the corresponding genomic clone and, if possible, determine the nature of the gene defect. Weaver and GC marker expression will be compared in GC and SN in normal and wv animals from embryonic into adult life.